Final answer:
The Free Soil Party, formed in 1848, advocated for preventing the spread of slavery to new territories and states. It aimed to attract moderate voters and protect northern interests against the influence of southern slaveholders.
Step-by-step explanation:
The political movement that advocated for any new territories entering the Union to be free states was the Free Soil Party. The Free Soil Party was formed in 1848 when antislavery leaders realized that the Liberty Party was not attracting moderate voters. They aimed to create a more competitive political force whose central belief was that the federal government should be divorced from slavery. The 1848 presidential election pitted the Free Soil Party against pro-slavery candidates from both the Whig and Democratic parties. Although they did not win the presidency, the Free Soil Party's influence was notable as they garnered a significant portion of the popular vote and even gained Congressional seats. This party emphasized the slogans 'Free Soil, Free Speech, Free Labor, and Free Men,' and focused on opposing the extension of slavery into new territories, reflecting the northern opposition to the perceived control of national politics by southern slaveholders aimed at protecting and extending slavery.